The overall objective of this proposal is to elucidate the mechanism by which pituitary hormones acting on the testis regulate the development and maintenance of normal Leydig cell function. We propose to investigate the regulation of both testosterone production and estrogen production. Studies planned or in progress include: 1) the role of prolactin, FSH and growth hormone per se as well as in combination with LH/hCG in acute stimulation of Leydig cell aromatization; 2) the dependence on RNA and protein synthesis on LH induced Leydig cell aromatization; 3) the effect of specific inhibitors of aromatization and of cholesterol-side chain cleavage on acute LH stimulation of testosterone synthesis and of aromatization; 4) the specific role of FSH, LH or prolactin on Leydig cell development during sexual maturation; 5) the relationship of LH receptors to Leydig cell responsiveness in Leydig cells purified by Metrizamide gradient centrifugation.